In a hydraulic shovel, a working machine is provided at a front part of an upper revolving superstructure, a counterweight is placed at a rear end portion of the upper revolving superstructure and a heavy-mass engine is placed in the vicinity of a front of the counterweight in order to be balanced with the working machine, and a cab seat is placed in front of the engine, in general. In order to simplify the explanation, the term, cab seat, is assumed to be a generic name of an occupied range of an operator, which includes a seat, a foot floor part which is in front of the seat for the operator to place his or her feet on, and an operating device having an operating lever and the like. When only the seat is to be indicated, it is distinguished from the cab seat by calling it as an operator seat. The same shall apply hereinafter.
According to the above-described constitution, there arises the problem that maintainability of the engine and its peripheral equipment is inhibited because a rear surface side of the engine is closed by the counterweight, and various kinds of means are conventionally considered to solve this problem. First, as a first prior art example, a structure, in which each part of a counterweight facing each of maintenance target parts of an engine, a main pump, a radiator and the like is constituted of a split counterweight attachable and detachable, and a maintenance operation can be performed from the ground by removing a corresponding split counterweight for each maintenance target part by a crane, is known (for example, pages 4 to 5, and FIG. 1 of Japanese Patent Laid-open No. 2001-106479).
As a second prior art example, a structure in which windows are provided at a center of a rear surface and a left and right side surfaces of the counterweight, maintenance inspection for the engine and the like is performed through the three windows, each window cover attached to the three windows has a rib plate with springiness on a back surface, and is fixed by engaging the rib plate in a groove of an inner perimeter of each window to make attachment and detachment easy, is known (for example, pages 2 to 3, and FIG. 2 of Japanese Patent Laid-open No. 2001-279722).
However, in the first prior art example, an operation of removing the split counterweight at the region facing the maintenance target part is required when the maintenance operation is performed. Further, a crane is required for detachment and attachment of the split counterweight, and the construction of connecting portions at the spots where the counterweight is split causes high cost, thereby causing the problem of making it difficult to apply the first prior art example to the counterweight of a compact hydraulic shovel operated in, for example, an urban area. In the second prior art example, the counterweight needs to be so large as the other parts can make up for large mass loss caused by opening the window portions because three windows as wide as to make the maintenance easy are provided on the counterweight, and therefore there is the problem that it is difficult to apply the second prior art example to the counterweight of a compact hydraulic shovel.
For the reason as described above, in a conventional compact hydraulic shovel, the height of the counterweight is generally restrained, an inspection cover is placed adjacently to an area above the counterweight to be openable and closable, and the engine is maintained from a position diagonally above over the counterweight by opening this inspection cover.
According to FIG. 5 to FIG. 7, a third prior art example of a counterweight according to the prior art will be explained with a rear end small revolving hydraulic shovel having a small revolving radius of an rear end being cited as an example of a compact hydraulic shovel. A hydraulic shovel 2 is loaded with an upper revolving superstructure 50 rotatably on a top portion of a base carrier 3. A locus of a revolving radius R of a rear end portion of the upper revolving superstructure 50 is structured to be within a lateral external width B of the base carrier 3.
The upper revolving superstructure 50 has a revolving frame 51 at a bottom portion. A working machine 5 is mounted at a front portion of the revolving frame 51 to be swingable up and down via a swing bracket 4 which is made laterally swingable by a swing cylinder 4a. For the purpose of keeping balance with the working machine 5, a counterweight 52 is placed at a rear end portion and an engine 13 is placed in the vicinity of a front of the counterweight 52, in a rear portion of the revolving frame 51. In order to make it possible to perform daily inspection and maintenance of the engine 13, a height H1 of the counterweight 52 is restrained, and an inspection cover 57 is mounted on a top portion of the counterweight 52 to be openable and closable in an up and down direction as shown by the chain double-dashed line in FIGS. 5 and 6.
A frame 53 is vertically provided at a top portion of the revolving frame 51, in the vicinity of the engine 13. A side surface partition wall 54, a top surface partition wall 55 and a front surface partition wall 56 for the engine 13 are respectively mounted to the frame 53. A cab seat 60 constituted of an operator seat 21, a floor frame 61 for supporting the operator sheet 21, and an operating lever 22 placed at a front portion of the floor frame 61 is provided in front of the front surface partition wall 56. An equipment room 58 is placed adjacently to a right side of the cab seat 60, and a fuel tank, a working fluid tank, a main operating valve and the like (none of them are shown) are placed in the equipment room 58. The compact upper revolving superstructure 50 is constituted of them.
However, in the third prior art example, there arise a few problems as a result of constituting the upper revolving superstructure 50 including the counterweight 52 to be compact though the working machine 5 protrudes forward to be long.
As a first problem, it is difficult to give sufficient allowance to the mass of the counterweight 52 as a result of restraining the height H1 of the counterweight 52. For this reason, when the equipment specification of the hydraulic shovel 2 is replaced corresponding to an operation site, for example, a bucket 6 at the tip end portion of the working machine 5 is replaced with an attachment of a different specification and the like, the frequency at which mounting of an additional counterweight 52A (shown by the chain double-dashed line in the drawing) is needed becomes high. On such an occasion, there is the possibility that a revolving radius RA of the rear end portion of the upper revolving superstructure 50 exceeds a lateral external width B of the base carrier 3. As a result, there arises the problem that the frequency, at which extra cost, complicated parts management and reduction in function occur, becomes high.
As a second problem, though the height H1 of the counterweight 52 is restrained, a lower rear surface side of the engine 13 is closed by the counterweight 52. Consequently, when, for example, a starter 13s of the engine 13, a compressor 13k when the air conditioner is loaded, and the like are mounted to the rear surface side (vehicle body rear portion side) of the engine 13, the counterweight 52 interferes with the maintenance operation of them and becomes the operation in the narrow space. As a result, there arises the problem that the maintainability of the engine 13 is not secured sufficiently.